Daniels et al, U.S. Pat. No. 3,949,073, disclosed the preparation of soluble collagen by dissolving tissue in aqueous acid, followed by enzymatic digestion. The resulting atelopeptide collagen is soluble, and substantially less immunogenic than unmodified collagen. It may be injected into suitable locations of a subject with a fibril-formation promoter (described as a polymerization promoter in the patent) to form fibrous collagen implants in situ, for augmenting hard or soft tissue. This material is now commercially available from Collagen Corporation (Palo Alto, Calif.) under the trademark Zyderm.RTM. Collagen Implant.
Miyata et al, U.S. Pat. No. 4,164,559, disclosed an ophthalmic drug delivery system comprising a chemically modified collagen thin membrane carrier. While these materials are clear, they do not have the mechanical strength required for ophthalmic devices such as lenticules, which are intended for long-term in vivo use.
Luck et al, U.S. Pat. No. 4,488,911, disclosed a method for preparing collagen in solution (CIS), wherein native collagen is extracted from animal tissue in dilute aqueous acid, followed by digestion with an enzyme such as pepsin, trypsin, or Pronase.RTM., a trademark of American Hoechst Corporation, Somerville, N.J. The enzymatic digestion removes the telopeptide portions of the collagen molecules, providing "atelopeptide" collagen in solution. The atelopeptide CIS so produced is substantially nonimmunogenic, and is also substantially non-crosslinked due to loss of the primary crosslinking regions. The CIS may then be precipitated by dialysis in a moderate shear environment to produce collagen fibers which resemble native collagen fibers. The precipitated, reconstituted fibers may additionally be crosslinked using a chemical agent (for example, aldehydes such as formaldehyde and glutaraldehyde), heat, or radiation. The resulting products are suitable for use in medical implants due to their biocompatability and reduced immunogenicity.
Wallace et al, U.S. Pat. No. 4,424,208, disclosed an improved collagen formulation suitable for use in soft tissue augmentation. Wallace's formulation comprises reconstituted fibrillar atelopeptide collagen (for example, Zyderm.RTM. Collagen) in combination with particulate, crosslinked atelopeptide collagen dispersed in an aqueous medium. The addition of particulate crosslinked collagen improves the implant's persistence, or ability to resist shrinkage following implantation.
Smestad et al, U.S. Pat. No. 4,582,640. disclosed a glutaraldehyde crosslinked atelopeptide CIS preparation (GAX) suitable for use in medical implants. The collagen is crosslinked under conditions favoring interfiber bonding rather than intrafiber bonding, and provides a product with higher persistence than non-crosslinked atelopeptide collagen. Said product is commercially available from Collagen Corporation under the trademark Zyplast.RTM. Collagen Implant.
Nguyen et al, U.S. Pat. No. 4,642,117, disclosed a method for reducing the viscosity of atelopeptide CIS by mechanical shearing. Reconstituted collagen fibers are passed through a fine-mesh screen until viscosity is reduced to a practical level for injection.
Nathan et al, U.S. Pat. No. 4,563,350, disclosed osteoinductive bone repair compositions comprising an osteoinductive factor, at least 5% nonreconstituted (afibrillar) collagen, and the remainder reconstituted collagen and/or mineral powder (e.g., hydroxyapatite). CIS may be used for the nonreconstituted collagen, and Zyderm.RTM. Collagen Implant (ZCI) is preferred for the reconstituted collagen component. The material is implanted in bone defects or fractures to speed ingrowth of osteoclasts and promote new bone growth.
Chu, U.S. Pat. No. 4,557,764, disclosed a "second nucleation" collagen precipitate which exhibits a desirable malleability and putty-like consistency. Collagen is provided in solution (e.g., at 2-4 mg/mL), and a "first nucleation product" is precipitated by rapid titration and centrifugation. The remaining supernatant (containing the bulk of the original collagen) is then decanted and allowed to stand overnight. The precipitated second nucleation product is collected by centrifugation.
Chu, U.S. Pat. No. 4,689,399, disclosed a collagen membrane preparation, which is prepared by compressing and drying a collagen gel. The resulting product has high tensile strength.
Silver et al., U.S. Pat. No. 4,703,108, disclosed the preparation of a sponge prepared by crosslinking insoluble/collagen using dehydrothermal means or by using cyanamide. Berg et at., U.S. Pat. No. 4,837,285, disclosed the preparation of collagen in bead form for soft tissue augmentation. Brodsky et al., U.S. Pat. No. 4,971,954, have disclosed a method of crosslinking collagen using ribose or other reducing sugars.
Miyata et al., Japartese patent application 63-256512, published Aug. 17, 1992, discloses a composition comprised of atelopeptide collagen linked to a polyepoxy compound. The composition is injected into the body to obtain sustained skin-lifting effects.
J. A. M. Ramshaw et al, Anal Biochem (1984) 141:361-65, and PCT application WO87/04078, disclosed the precipitation of bovine collagen (types I, II, and III) from aqueous PEG solutions, where there is no binding between collagen and PEG.
Werner, U.S. Pat. No. 4,357,274, disclosed a method for improving the durability of sclero protein (e.g., brain meninges) by soaking the degreased tissue in hydrogen peroxide or polyethylene glycol for several hours prior to lyophilization. The resulting modified whole tissue exhibits increased persistence.
Hiroyoshi, U.S. Pat. No. 4,678,468, disclosed the preparation of polysiloxane polymers having an interpenetrating network of water-soluble polymer dispersed within. The water-soluble polymer may be a collagen derivative, and the polymer may additionally include heparin. The polymers are shaped into artificial blood vessel grafts, which are designed to prevent clotting.
Other patents disclose the use of collagen preparations incorporating bone fragments or minerals. For example, Miyata et al, U.S. Pat. No. 4,314,380, disclosed a bone implant prepared by baking animal bone segments, then soaking the baked segments in a solution of atelopeptide collagen. Deibig et at, U.S. Pat. No. 4,192,021, disclosed an implant material which comprises powdered calcium phosphate in a pasty formulation with a biodegradable polymer (which may be collagen). Commonly owned U.S. application Ser. No. 06/855,004, filed Apr. 22, 1986, now abandoned, disclosed a particularly effective bone repair material comprising autologous bone marrow, collagen, and particulate calcium phosphate in a solid, malleable formulation.
There are several references in the an to proteins modified by covalent conjugation to polymers to alter the solubility, antigenicity, and biological clearance of the protein. For example, U.S. Pat. No. 4,261,973 disclosed the conjugation of several allergens to PEG or PPG (polypropylene glycol) to reduce the proteins' immunogenicity. U.S. Pat. No. 4,301,144 disclosed the conjugation of hemoglobin with PEG and other polymers to increase the protein's oxygen-carrying capability. EP O98110 disclosed coupling an enzyme or interferon to a polyoxyethylene-polyoxypropylene (POE-POP) block polymer to increase the protein's half-life in serum. U.S. Pat. No. 4,179,337 disclosed conjugating hydrophilic enzymes and insulin to PEG or PPG to reduce immunogenicity. Davis et al, Lancet (1981) 2:281-83, disclosed the enzyme uricase modified by conjugation with PEG to provide uric acid metabolism in serum having a long half-life and low immunogenicity. Nishida et al, J Pharm Pharmacol (1984) 36:354-55, disclosed PEG-uricase conjugates administered orally to chickens, demonstrating decreased serum levels of uric acid. Inada et al, Biochem & Biophys Res Comm (1984) 122:845-50 disclosed lipoprotein lipase conjugated with PEG to render it soluble in organic solvents. Takahashi et al, Biochem & Biophys Res Comm (1984) 121:261-65, disclosed HRP conjugated with PEG to render the enzyme soluble in benzene. Abuchowski et al, Cancer Biochem Biophys (1984) 7:175-86, disclosed that enzymes such as asparaginase, catalase, uricase, arginase, trypsin, superoxide dismutase, adenosine deaminase, phenylalanine ammonia-lyase and the like conjugated with PEG exhibit longer half-lives in serum and decreased immunogenicity. However, these references are essentially concerned with modifying the solubility and biological characteristics of proteins administered in low concentrations in aqueous solution.
M. Chvapil et al, J Biomed Mater Res (1969) 3:315-32, disclosed a composition prepared from collagen sponge and a crosslinked ethylene glycol monomethacrylate-ethylene glycol dimethacrylate hydrogel. The collagen sponge was prepared by lyophilizing an aqueous mixture of bovine hide collagen and methylglyoxal, a tanning agent. The sponge-hydrogel composition was prepared by polymerizing ethylene glycol monomethacrylate and ethylene glycol dimethacrylate in the sponge.
A series of related patents disclose various types of collagen-containing materials. The patents are U.S. Pat. Nos. 4,703,108, issued Oct. 27, 1987; 4,861,714, issued Aug. 29, 1989; 4,863,856, issued Sep. 5, 1989; 4,925,924, issued May 15, 1990; 4,970,298, issued Nov. 13, 1990; and 4,997,753, issued Mar. 5, 1991. All of these patents disclose collagen materials wherein type I, II, and III collagens are contacted with a crosslinking agent selected from the group consisting of a carbodiimide or a succinimidyl active ester. Various types of treatment may be carried out prior to or after crosslinking in order to form particular types of desired materials such as sponges and/or sheets.
In commonly owned U.S. Pat. No. 5,162,430, issued Nov. 10, 1992, we described conjugates whereby atelopeptide collagen is covalently crosslinked with synthetic hydrophilic polymers such as polyethylene glycol. Such conjugates are useful for a variety of applications, such as soft tissue augmentation and the formation of implants useful in bone repair. In U.S. application Ser. No. 07/922,541, we disclose various activated forms of polyethylene glycol and various linkages which can be used to produce collagen-synthetic polymer conjugates having a range of physical and chemical properties. We now describe collagen-synthetic polymer conjugates formed using chemically modified forms of collagen, which impart to the conjugate specific properties, such as optical clarity and mechanical strength, making the conjugates particularly useful in devices for use in ophthalmic applications.